The present invention is directed to antibiotic compounds having a superior combination of properties.
Echinocandin B and related fermentation metabolites are known to have antifungal properties when tested in vitro. However, some of the compounds are toxic when tested in vivo and some show lytic activity on human red blood cells thus rendering them undesirable for therapeutic use. Some derivatives have been prepared in a search to find more useful compounds for human therapeutic use. Most of the derivatives are lipophilic side chain analogs at the .alpha.-amino-nitrogen of the hydroxyornithine residue or ethers at the hemiaminal position. A number of aminoalkyl ethers were prepared and are the subject of Belgian patent No. 859,067 (1978) and Belgian patent No. 851,310 (1977).
According to the present invention it has been discovered that when the aminoalkyl ether is that derived not from echinocandin B but from a cyclohexapeptide compound in which one of the nuclear amino acids is glutamine instead of threonine, the compound has superior antibiotic activity in vivo. Moreover, the compound is substantially non-toxic and also non-lytic toward human blood cells, thereby rendering the compound adaptable for human therapy which has. not been possible with many compounds even though they might be active.
The compounds of the present invention are aminoalkyl ethers at the 5-position of ornithine and acyl derivatives at the N.sup.2 position of the ornithine in the cyclopeptide nucleus and which may be represented by the formula (I) (SEQ ID NO 1) ##STR3## In this and succeeding formulas, ##STR4## wherein n is 2 to 6; ##STR5##
Salts of the foregoing are also within the scope of the present invention. Salts include acid addition salts and quaternary ammonium salts. These salts are formed at the amino function of the amino alkyl group.
Pharmaceutically acceptable salts as acid addition salts are those from acids such as hydrochloric, hydrobromitc, phosphoric, sulfuric, maleic, citric, acetic, tartaric, succinic, oxalic, malic, glutamic, salicylic, lactic, gluconic, hydrocarbonic and the like, and include other acids related to the pharmaceutically acceptable salts listed in Journal of Pharmaceutical Science, 66, 2 (1977).
The compounds in the scope of the present invention which have a highly desirable combination of properties of high effectiveness and/or low toxicity and other adverse side reactions are all aminoalkyl ethers at the 5-hydroxy position of the 4,5-dihydroxyornithine component of the cyclopeptide. The amino group may be substituted or the alkyl portion may have other substituents but it is critical that the basic amino property of the group be retained.
The acyl substituent on the ornithine nitrogen may be varied from that of the natural product. Thus, the side chain radical which together with carbonyl forms the acyl group may be alkoxy substituted phenyl or naphthyl as well as being derived from a long chain fatty acid.
Certain compounds may be named as echinocandins or pneumocandins. The pneumocandins, compounds in which one of the amino acids of the cyclic peptide is glutamine instead of a second threonine and the side chain on the ornithine nitrogen is 10,12-dimethylmyristoyl have been named as pneumocandins by Schwartz et al, J. Antibiot. 45, No. 12, 1853-1866 (1992), and also found in J. M. Balkovec et al, Tetrahedron Let., 1992, 33, 4529-32. Thus, the natural product in which the nucleus is 4,5-dihydroxyornithine, threonine, 4-hydroxyproline, 3,4-dihydroxyhomotyrosine, 3-hydroxy glutamine and 3-hydroxyproline and the side chain is 10,12-dimethylmyristoyl is named pneumocandin B.sub.0. Compounds of the present invention which differ only in the substituent at the 5-hydroxy of ornithine may be named as derivatives of pneumocandin B.sub.0 although for the compound of the parent application which was named as an echinocandin, the echinocandin name is given.
The compounds of the present invention are white solids soluble in a variety of organic solvents such as methanol, ethanol, dimethylformamide (DMF), dimethylsulfoxide (DMSO) and the like and also in water.
The antibiotic activity disclosed above is especially of note against fungi causing pathogenic mycotic infections such as Candida albicans, Candida tropicalis, and the like, Aspergillus fumigatus and other Aspergillus sp. Compound I has been found to significantly prolong the survival of mice infected with Candida albicans and also to eradicate Candida albicans from kidneys of experimentally infected mice. These properties point to a new antifungal drug with great potential in the therapy of human mycotic infections. Additionally, the compound is adapted to be employed for inhibiting or alleviating Pneumocystis carinii infections, prevalent in immune compromised patients and which have usually been fatal.
The structural aspect which distinguish the compounds of the present invention and which confer the foregoing desirable properties is the combination of the aminoalkyl group on the 5-hydroxyornithine of the cyclopeptide nucleus and the carboxamide group arising from the nuclear amino acid glutamine. For the desirable combination of properties, the amino acids of the nucleus are not changed. The aminoalkyl group may be varied provided that the aminoalkyl always has a basic amino group and certain acyl groups may replace the 10,12-dimethylmyristoyl group on the .alpha.-nitrogen of the ornithine, but these modifications are those which do not affect the fundamental and essential amino acids of the cyclopeptide.
The compounds of the present invention may be prepared by aminoalkylation of a natural product cyclopeptide or a derivative of a natural product which is represented by the formula (A) (SEQ ID NO. 1) ##STR6## with an aminoalkanol (or alkanolamine), R.sub.1 OH wherein R.sub.1 is an aminoalkyl group in which the amino may be substituted or unsubstituted. When it is a substituted amino group, the substituent is such that it does not neutralize the basic amino group. The aminoalkylation is carried out in the presence of a strong acid in an aprotic polar solvent and the product isolated from the reaction mixture preferably by the use of reverse phase high performance liquid chromatography (HPLC).
The nucleus of the aminoalkyl ether and the starting material are the same since the amino acids of the peptide nucleus are not changed. Thus, both product and starting material have the same Sequence ID number.
R.sub.1 OH may be substituted or unsubstituted. When unsubstituted, a protecting group optionally is placed on the amino group before the reaction is carried out and the protecting group removed after the etherification is complete as hereinafter more fully described. When R.sub.1 is a substituted amino group, a substituted amino alcohol may be the reactant or alternatively an unsubstituted amino alcohol may be employed and the substituent subsequently put on the amino group.
The amino alcohol is generally employed in the form of an acid addition salt and is employed in an amount of from about 20 to 200 equivalents.
The reaction is carried out in the presence of a strong acid. Examples of strong organic acids are camphorsulfonic acid, p-toluenesulfonic acid, methanesulforiic acid or a mineral acid such as hydrochloric or hydrobromic acid. Hydrochloric and camphorsulfonic acids are preferred. Approximately 1 equivalent of the acid is employed.
A solvent is employed in carrying out the reaction. Suitable solvents are aprotic solvents and include dimethylsulfoxide (DMSO), dimethylformamide (DMF), 1-methyl-2-pyrrolidinone, hexamethylphosphoric triamide (HMPA), dioxane or combinations thereof. Dimethyl sulfoxide and dimethylformamide is preferred.
When the amino alcohol has a primary amino group, the group may be protected before it is used. Conventional protecting groups are employed. The carbobenzyloxy group (CBz) is the preferred group. In protecting the amino group with a carbobenzyloxy group, the group is placed on the amino group of R.sub.1 OH by conventional means and the protected R.sub.1 OH, the cyclopeptide to be etherified and a strong acid, as used in the etherification using an unprotected R.sub.1 OH, are stirred together in a solvent such as those useful in the reaction employing an unprotected amino alcohol until substantial completion of the reaction. The progress of the reaction may be monitored by HPLC. After completion of the reaction, the reaction mixture is neutralized, diluted with water and then purified by HPLC to obtain an N-benzyloxycarbonyl aminoalkyl ether intermediate.
To obtain the desired aminoalkyl ether, the protected ether is hydrogenated under balloon pressure in the presence of palladium/carbon in acetic acid, preferably for from one to several hours as may be monitored by analytical HPLC with 30 to 40 percent aqueous acetonitrile solvent system containing 0.1% trifluoroacetic acid. The product is then recovered by first removing the catalyst and lyophilizing the filtrate to obtain the desired product as acetate salt. The latter may be converted to a hydrochloride by passing a minimum volume aqueous solution thereof through an anion exchange column.
With substituted amino groups, if the substituent is not already on the amino alcohol, it may be placed on the amino group after the ether is formed by a method appropriate for the particular group and within the knowledge of the skilled in the art.
The ether product is isolated from the reaction mixture and is conveniently purified using HPLC techniques, including utilization of a reverse phase column. The eluants from HPLC are then concentrated and lyophilized as subsequently detailed. The elution is carried out using various concentrations of acetonitrile/water, starting at about 15 percent acetonitrile and then increasing the amount of acetonitrile. The eluting solutions generally contain 0.1 percent trifluoroacetic acid (TFA) or acetic acid and the product on isolation is found in the form of the salt.
When quaternary ammonium salts are desired, the amino alkyl product is reacted with excess alkyl halide by stirring in a conventional manner until substantial amounts of the product is obtained, the reaction mixture diluted with water and chromatographed according to conventional procedures.
The compounds of the present invention are active against many fungi and as previously indicated particularly against Candida species. The antifungal properties may be illustrated with the minimum fungicidal concentration (MFC) determination against certain Candida organisms in a microbroth dilution assay carried out in a Yeast Nitrogen Base (Difco) medium with 1 percent dextrose (YNBD).
In carrying out the assay, Compound I was solubilized in 10 percent dimethyl sulfoxide (DMSO) and diluted to 2560 .mu.g/ml. The compound was then diluted to 256 .mu.g/ml in YNBD. 0.15 mL of the suspension was dispensed to the top row of a 96-well plate (each well containing 0.15 ml of YNBD) resulting in a drug concentration of 128 .mu.g/ml. Two-fold dilutions were then made from the top row to obtain final drug concentrations ranging from 128 to 0.06 .mu.g/ml.
The yeast cultures, maintained on Sabouraud dextrose agar were transferred to YN broth (Difco) and incubated overnight at 35.degree. C. with shaking (250 rpm). After incubation, each culture was diluted in sterile water to yield a final concentration of 1-5.times.10.sup.6 colony forming units (CFU)/ml.
96-well microplates were inoculated using a MIC-2000 (Dynatech) which delivers 1.5 ml per well yielding a final inoculum per well of 1.5-7.5.times.10.sup.3 cells. The microplates were incubated at 35.degree. C. for 24 hours. The minimum inhibitory concentrations (MICs) were recorded as the lowest concentrations of drug showing no visible growth.
After recording the MIC, the plates were shaken to resuspend the cells. Thereafter, 1.5 .mu.l samples from the wells in the 96-well microplate were transferred to a single well tray containing Sabouraud dextrose agar. The inoculated trays were incubated 24 hours at 28.degree. C. and then read for minimum fungicidal concentration (MFC). MFC is defined as the lowest concentration of drug showing no growth or less than 4 colonies per spot. The results showed the minimum fungicidal concentration against Candida albicans MY 1055 and against Candida tropicalis MY 1012 to be as follows:
______________________________________ MFC .mu.g/mL C. C. tropi- albicans calis MY MY R.sub.1 R.sub.2 1055 1012 ______________________________________ --CH.sub.2 CH.sub.2 --NH--C(.dbd.NH)NH.sub.2 DMTD* 0.125 0.125 --CH.sub.2 CH.sub.2 N.sup.+ (CH.sub.3).sub.3 I.sup.- DMTD 0.25 0.25 --CH.sub.2 CH.sub.2 NHCOCH.sub.2 NH.sub.2 DMTD 1.0 0.5 --CH.sub.2 CH.sub.2 NH.sub.2 DMTD 0.125 0.25 --CH.sub.2 CH.sub.2 NH.sub.2 C.sub.6 H.sub.4 OC.sub.8 H.sub.17 (p) 0.5 0.5 ______________________________________ *DMTD = 9,11dimethyltridecyl
In a separate similar experiment with different compounds against Candida albicans MY 1750, the following results were obtained:
______________________________________ MFC .mu.g/mL R.sub.1 R.sub.2 C. albicans MY 1750 ______________________________________ --CH.sub.2 CH(NH.sub.2)CH.sub.3 DMTD 0.50 --CH.sub.2 CH.sub.2 NHC.sub.2 H.sub.5 DMTD 0.50 --CH.sub.2 CH(OH)CH.sub.2 NH.sub.2 DMTD 0.50 --CH.sub.2 CH.sub.2 NH--C(.dbd.NH)CH.sub.3 DMTD 0.25 --CH.sub.2 CH.sub.2 NHCOCH.sub.2 NH.sub.2 DMTD 0.50 --CH.sub.2 CH(NH.sub.2)CH.sub.2 NH.sub.2 DMTD 2.0 ______________________________________
The compounds also show in vivo effectiveness against fungi as seen by the following experiment carried out on the compound on which R.sub.1 is --CH.sub.2 CH.sub.2 NH.sub.2.
Growth from an overnight SDA culture of Candida albicans MY 1055 was suspended in sterile saline and the cell concentration determined by hemacytometer count and the cell suspension adjusted to 3.75.times.10.sup.5 cells/ml. Then 0.2 milliliter of this suspension was administered I.V. in the tail vein of mice so that the final inoculum was 7.5.times.10.sup.4 cells/mouse.
The assay then was carried out by administering aqueous solutions of Compound I (R.sub.1 =--CH.sub.2 CH.sub.2 NH.sub.2) at various concentrations intraperitoneally (I.P.), twice daily (b.i.d.) for four consecutive days to 18 to 20 gram female DBA/2 mice, which previously had been infected with Candida albicans (MY 1055) in the manner described above. Distilled water was administered I.P. to C. albicans challenged mice as controls. After seven days, the mice were sacrificed by carbon dioxide gas, paired kidneys were removed aseptically and placed in sterile polyethylene bags containing 5 milliters of sterile saline. The kidneys were homogenized in the bags, serially diluted in sterile saline and aliquots spread on the surface of SDA plates. The plates were incubated at 35.degree. C. for 48 hours and yeast colonies were enumerated for determination of colony forming units (CFU) per-gram of kidneys. Compound I showed greater than 99 percent reduction of recoverable Candida CFUs at 0.4 mg/kg I.P. twice daily for four consecutive days.
A harmful and potentially fatal side reaction of a number of drugs including certain antibiotically active echinocandin compounds is red blood cell lysis. It is of particular interest that representative compounds of this invention exhibit no red blood cell lysis at concentrations far beyond what would be used for therapeutic purposes. The blood cell lysis property may be seen in the determination carried out in the following manner.
The blood employed is a 4 percent suspension of freshly drawn heparinized blood prepared by adding 2 milliliters of blood to 50 milliliters of sterile 5 percent dextrose.
Compoufid I was solubilized in a small volume of dimethylsulfoxide (DMSO) that was then diluted with distilled water to a final concentration of 5 percent DMSO to obtain a drug solution of 4.0 mg/ml. A 0.2 milliliter amount of the drug solution was added to 1.4 milliliters of sterile 5 percent dextrose to obtain the test solution. A diluent control was also prepared.
A 96-well microtiter plate with a well volume of 0.35 ml was used for the assay. Columns 2-12 were filled with 150 .mu.1 of sterile 5 percent dextrose. Then, 300 .mu.l of test solutions were dispensed into the wells in column 1 and serially two-fold diluted in 5 percent dextrose to yield final test concentrations of from 400 to 0.20 .mu.g/ml. 38 .mu.l of red blood cell suspension were added to each well, the plate was gently agitated to mix the well contents and incubated at room temperature for 2 hours, and thereafter observed to determine extent of hemolysis as indicated by complete or partial clearing (lysis).
Minimum lytic concentration (MLC) defined as the lowest concentration of test compound to produce complete or partial lysis of red blood cells was found for representative compounds against human blood cells to be as seen in the following table:
______________________________________ MLC R.sub.1 R.sub.2 (.mu.g/ml) ______________________________________ --CH.sub.2 CH(NH.sub.2)CH.sub.3 DMTD 400 --CH.sub.2 CH.sub.2 NHC.sub.2 H.sub.5 DMTD &gt;400 --CH.sub.2 CH(OH)CH.sub.2 NH.sub.2 DMTD &gt;400 --CH.sub.2 CH.sub.2 NHC(.dbd.NH)CH.sub.3 DMTD 200 --CH.sub.2 CH.sub.2 NHCOCH.sub.2 NH.sub.2 DMTD &gt;400 ______________________________________
The compounds of the present invention may also be useful for inhibiting or alleviating Pneumocvstis carinii infections in immune compromised patients. The efficacy of the compounds of the present invention for the therapeutic or anti-infective purposes may be demonstrated in studies on immunosuppressed rats in which Sprague-Dawley rats (weighing approximately 250 grams) are immunosuppressed with dexasone in the drinking water (2.0 mg/L) and maintained on a low protein diet for seven weeks to induce the development of pneumocystis pneumonia from a latent infection. Before drug treatment, two rats are sacrificed to confirm the presence of Pneumocystis carinii pneumonia (PCP). Five rats (weighing approximately 150 grams) are injected twice daily for four days subcutaneously (sc) with Compound I in 0.25 ml of vehicle (distilled water). A vehicle control is also carried out. All animals continue to receive dexasone in the drinking water and low protein diet during the treatment period. At the completion of the treatment, all animals are sacrificed, the lungs are removed and processed, and the extent of disease determined by microscopic examination of stained slides for the presence of cysts. The prevention of or reduction of cysts are seen in slides of lungs of treated rats when compared with the number of cysts in lungs of untreated controls or solvent controls.
The dosage required for 90 percent reduction of cysts with representative compounds may be seen in the following table:
______________________________________ R.sub.1 R.sub.2 mg/kg ______________________________________ --CH.sub.2 CH(NH.sub.2)CH.sub.3 DMTD &lt;0.08 --CH.sub.2 CH.sub.2 NHC.sub.2 H.sub.5 DMTD 0.04 --CH.sub.2 CH.sub.2 NHC(.dbd.NH)CH.sub.3 DMTD &lt;0.08 --CH.sub.2 CH.sub.2 NHCOCH.sub.2 NH.sub.2 DMTD 0.04 ______________________________________
The outstanding properties are most effectively utilized when the compound is formulated into novel pharmaceutical compositions with a pharmaceutically acceptable carrier according to conventional pharmaceutical compounding techniques.
The novel compositions contain at least a therapeutic antifungal or antipneumocystis amount of the active compound. Generally, the composition contains at least 1% by weight of Compound I or one of the components. Concentrate compositions suitable for dilutions prior to use may contain 90% or more by weight. The compositions include compositions suitable for oral, topical, parenteral (including intraperitoneal, subcutaneous, intramuscular, and intravenous), nasal, and suppository administration, or insufflation. The compositions may be prepacked by intimately mixing Compound I with the components suitable for the medium desired. Compositions formulated for oral administration may be a liquid composition or a solid composition. For liquid preparations, the therapeutic may be formulated with liquid carriers such as water, glycols, oils, alcohols, and the like, and for solid preparations such as capsules and tablets, with solid carriers such as starches, sugars, kaolin, ethyl cellulose, calcium and sodium carbonate, calcium phosphate, koalin, talc, lactose, generally with lubricant, such as calcium stearate, together with binders disintegrating agents and the like. Because of their ease in administration, tablets and capsules represent the most advantageous oral dosage form. It is especially advantageous to formulate the compositions in unit dosage form (as hereinafter defined) for ease of administration and uniformity of dosage. Compositions in unit dosage form constitute an aspect of the present invention and for injection take such forms as suspensions, solutions or emulsions in oily or aqueous vehicles such as 0.85 percent sodium chloride or 5 percent dextrose in water and may contain formulating agents such as suspending, stabilizing and/or dispersing agents. Buffering agents as well as additives such as saline or glucose may be added to make the solutions isotonic. The compound also may be solubilized in alcohol/propylene glycol or polyethylene glycol for drip intravenous administration. The compositions also may be presented in unit dosage form in ampoules or in multidose containers, preferably with added preservative. Alternatively, the active ingredients may be in powder form for reconstituting with a suitable vehicle prior to administration.
The term "unit dosage form" as used in the specification and claims refer to physically discrete units, each unit containing a predetermined quantity of active ingredient calculated to produce the desired therapeutic effect in association with the pharmaceutical carrier. Examples of such unit dosage forms are tablets, capsules, pills, powder packets, wafers, measured units in ampoules or in multidose containers and the like. A unit dosage of the present invention will generally contain from 10 to 200 milligrams of one of the compounds.
When the compound is for antifungal use any method of administration may be employed. For treating mycotic infections, oral administration is frequently preferred.
When the compound is to be employed for control of pneumocystis infections, it is desirable to directly treat lung and bronchi. For this reason inhalation methods are preferred. For administration by inhalation, the compounds of the present invention are conveniently delivered in the form of an aerosol spray presentation from pressurized packs or nebulisers. The preferred delivery system for inhalation is a metered dose inhalation (MDI) aerosol which may be formulated as a suspension of Compound I in a suitable propellant such as fluorocarbon or hydrocarbons.